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Looking for the V2 Hardware Upgrade Info

 

There was once a document sent out to owners that provided information on upgrading the V2 PCB to prevent MOSFET failure of the IRFZ24Ns, etc.
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Could someone send me a copy or provide on the wiki?
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Thanks
JJ
 

I don't have the document, but it was basically to put in the diodes that you can read about in slide #15 of this talk:
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There are other "gotchas" however, so might consider this list:
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Gordon KX4Z
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Here you go JJ

I was finally able to return a small favor for all your hard work on these awesome radios…

David
WK4DS?

On Thu, Feb 27, 2025 at 18:30 JJ - W9JES via <jj=[email protected]> wrote:
There was once a document sent out to owners that provided information on upgrading the V2 PCB to prevent MOSFET failure of the IRFZ24Ns, etc.
?
Could someone send me a copy or provide on the wiki?
?
?
Thanks
JJ
 

As far as I remember, several people tried several solutions that were discussed in the forum. Personally, I implemented a different version, a more complicated solution. This involves more work and may be alarming for those who do not like DIY. If my memory serves me correctly, I read it on the F5NPV website, which worked for me. By the way, v2 started with a mechanical defect, which was fixed by the manufacturer. Mounting the IRFZ24 to the heatsink was problematic.?
--
Gyula HA3HZ
 

On Fri, Feb 28, 2025 at 06:14 AM, WK4DS wrote:
Here you go JJ
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I was finally able to return a small favor for all your hard work on these awesome radios…
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David
WK4DS?
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Thanks David. Although this doesn't address the necessary upgrades to keep the IRFZ24Ns in place; it does help to convert a V2 to a V3.
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JJ,
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I do not have the documentation; I have only the GitHub files with the original V2 schematic. The zip file is attached.
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73
Evan
AC9TU
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sbitx-main v2.zip
sbitx-main v2.zip

 

One of the things to change is R201-R204 to 330ohm 1/4 resistors, I remember doing mine but I don't remember why, other than that I don't recall doing anything else.
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Joel
N6ALT
 

Joel,
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FYI, changing the resistors increased the bias current on the PIN diodes for the LPF and T/R switching diodes.? This was to reduce spurs and improve power output,
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73
Evan
AC9TU
 

This is from Farhan re upgrading my V2, "The standing current in the diodes that switch the LPFs was found insufficient on 3.5 MHz, hence, the resistors R201, R202,
R203 and R204 are changed from 470 ohms to 330 ohms."
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Joel
N6ALT
 

I misunderstood you, I thought this was what you was searching for. Swing and a miss I guess. Haha

David

On Fri, Feb 28, 2025 at 12:56 JJ - W9JES via <jj=[email protected]> wrote:
On Fri, Feb 28, 2025 at 06:14 AM, WK4DS wrote:
Here you go JJ
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I was finally able to return a small favor for all your hard work on these awesome radios…
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David
WK4DS?
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Thanks David. Although this doesn't address the necessary upgrades to keep the IRFZ24Ns in place; it does help to convert a V2 to a V3.
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On Fri, Feb 28, 2025 at 03:05 PM, WK4DS wrote:
I misunderstood you, I thought this was what you was searching for. Swing and a miss I guess. Haha
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David
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It's all good. Your information was useful for those who want to fully convert their V2 board to V3. Thank you.
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I think some folks misunderstood what I was asking for.?

The sBitx V2 has IRFZ24N MOSFETs. We want to continue to use them for the finals. What mods have to be performed to prevent oscillations and early MOSFET failures?
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Thanks.
 

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JJ, that’s hard to say. ?I had huge Zener’s in mine, and I still lost a MOSFET with no obvious reason. I cannot guarantee it at that instant, but I had not seen any oscillations ever in my unit since whatever updates were done. ??

I decided to go ahead and put in the TVS diodes that Ashhar suggested and I also switched to 100 V IRF 520s. ? I searched for any isolations and did not see any with this new set up. I have not had enough operating time to guarantee this, but I suspect it will be satisfactory.

I have just about the same output with the 520s and I’m happier with them?



Gordon kx4z?




On Feb 28, 2025, at 16:57, JJ - W9JES via groups.io <jj@...> wrote:

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I think some folks misunderstood what I was asking for.?

The sBitx V2 has IRFZ24N MOSFETs. We want to continue to use them for the finals. What mods have to be performed to prevent oscillations and early MOSFET failures?
?
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Thanks.
 

JJ,
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I agree with Gordon's suggestions.? IRF520 would be a more robust part, and the TVS protection is a good idea as the driver circuit can deliver higher than the gate voltage if driven to full power.
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Also, Joel suggests that the pin diode current should be increased by 470 to 330 ohm replacements.? The bias increase is another good idea.
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Another suggestion is to add the resistors to the drain of Q101 and series with D20 and D21.? Gordon posted this here:
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You should verify the signal purity before putting it in the air.
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73
Evan
AC9TU
 

On Fri, Feb 28, 2025 at 10:57 PM, JJ - W9JES wrote:
I think some folks misunderstood what I was asking for.?

The sBitx V2 has IRFZ24N MOSFETs. We want to continue to use them for the finals. What mods have to be performed to prevent oscillations and early MOSFET failures?
?
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Thanks.
No documentation was sent about any changes to the v2.
What happened was that the devices sent in April 2023 did not come with any information sheet, so on May 3rd, several messages came, which can be found on the sbitx.net page, how to set the performance and some similar information. The hardware modification was discussed on the forum and no information was released about the change.
So whoever modified it did it according to their own thoughts.
My own experience with the v2, which uses IRFZ24N FETs in the output stage:

1. I checked the electrical and mechanical connections of the device and repaired them as necessary. (FET clamper broke / D27 diode was faulty, so I replaced the power/swr diodes together / Bias adjustment was difficult, so I modified the circuit (see F5NPV website) / I replaced the mica insulator with Aluminum Nitride for better heat conduction / I cool the power stage heatsink with an external 92x92x25mm silent fan / I cool the RPi4 from the back with a 50x50x10mm fan fixed on an intermediate board / I use the PTT control of the power stage based on the designs of KX4Z Gordon Furthermore

2. I use the device with a current limit of 12.5V and 6.5 A, because it was not in use yet and I powered it from a battery, with a dummy load instead of an antenna, then one of the FETs of the power stage became shorted. The replaced and selected FETs have been working fine ever since!
Currently more than 8800 QSOs and these FETs have 168/150 dxcc/lotw since November 16, 2023.

3. I use a single antenna on 3 bands. This is a vertical delta loop antenna installed obliquely. There are two ferrite rings at the feed point (about 10 meters high).
One is for 100/50 Ohm and the other is for symmetrical/asymmetrical impedance matching.
I sized the 42.8 meter wire to 7 MHz, which can also be used at 14 and 21 MHz without an antenna tuner.

4. I consider myself a returning amateur radio operator because of sbitx, because I previously dismantled my antennas (2 el 5 band QQ, 20.8m high vertical) and I made this antenna only for sbitx, so that I could use it.

5. Most importantly, if it weren't for the amateurs who brought the development to the current level, I probably wouldn't be a device owner.
So a huge thank you to them for their continuous efforts to fix the bugs they find.
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That's all for my v2 story.
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Gyula HA3HZ

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